This subproject is one of many research subprojects utilizing the resources provided by a Center grant funded by NIH/NCRR. The subproject and investigator (PI) may have received primary funding from another NIH source, and thus could be represented in other CRISP entries. The institution listed is for the Center, which is not necessarily the institution for the investigator. It is well-known that hypoxic or even anoxic regions in solid-growing tumors may limit the efficacy of non-surgical therapy, including radiotherapy, photodynamic therapy, chemotherapy. Accurate assessment of tumor oxygenation at various stages of tumor growth and in response to interventions/therapy may provide a better understanding of tumor development and may serve as a prognostic indicator for treatment outcome, potentially allowing individualized cancer therapy. We have recently identified a 1H MRI probe of pO2: hexamethyldisiloxane (HMDSO). The PI has developed a new, HMDSO-based quantitative MR oximetry technique PISTOL (Proton Imaging of Silanes to Map Tissue Oxygenation Levels) for mapping of tissue interstitial pO2. This technique has been applied to study the tumor microenvironmenental response to therapy in this project. The goal of the first subproject is to optimize synthesis and characterization of HMDSO based nanoemulsions as pO2 nanoprobes (funding source 1) for 1H MRI based oximentry and uses them to study tumor response to combination chemotherapy. The goal of the second subproject (funding source 2) is to study the response of combining hyperbaric oxygen with pO2-sensitive photodynamic therapy of cancer with pO2 nanoprobes.